Hi,

When attempting to run cargo fmt on a the ill-typed (or maybe not even parsable?) library consisting of two files:

lib.rs:

mod foo;

foo.rs

const BAR = 42;

the compiler unexpectedly panics due to a failed assertion:

thread 'main' panicked at compiler/rustc_errors/src/lib.rs:565:9:
assertion failed: self.stashed_diagnostics.is_empty()

with rustc 1.78.0-nightly (fc3800f65 2024-02-26). Full stack-trace:

rustc-ice-2024-02-27T19_28_13-1514879.txt

I'm happy to work on this, but I'm a bit clueless as to what the issue is.